Water bears might end up being the last animals on Earth.
Also known as tardigrades, these microscopic creatures are tough. A new study concludes that they could survive until — several billion years from now — the sun boils Earth’s oceans away.
That’s good news for anyone hoping Earthlings may have company in the universe. If these critters can live through such extreme conditions on our planet, it suggests life might exist in other seemingly inhospitable places.
Other studies had looked at threats to people from space. They focused on such things as asteroids striking Earth, neighboring stars going supernova or huge explosions called gamma-ray bursts. But for the new study, researchers ignored fragile humans. They wanted to know what it would take to wipe out one of the world’s ultimate survivors.
So they turned to tardigrades.
The microscopic critters live all around they world. And they are hardy. Decades without food or water? No problem. Temperatures plummeting to –272° Celsius (–460° Fahrenheit) or skyrocketing to 150 °C (300 °F)? Bring it on. Even the crushing pressure of deep seas doesn’t bother them. Nor does the vacuum of outer space or exposure to extreme radiation.
Water bears are so sturdy that even a nuclear war probably wouldn’t kill them. Neither would global warming nor any astronomical events that wreak havoc on Earth’s atmosphere. But all of these scenarios could doom humans, notes Avi Loeb. He’s an astrophysicist at Harvard University in Cambridge, Mass.
To exterminate tardigrades, something would have to boil the oceans away. (No more water means no more water bears.) So Loeb and his colleagues calculated just how big an asteroid, how strong a supernova, or how powerful a gamma-ray burst would have to be to heat Earth’s oceans that much.
“They actually ran the numbers on everyone’s favorite natural doomsday weapons,” says Seth Shostak. He’s an astronomer at the SETI Institute in Mountain View, Calif. (One of the SETI Institute’s goals is to search for alien life.)
Loeb’s team found that there are only 19 asteroids in the solar system massive enough to wipe out water bears. None are on a collision course with Earth.
A supernova — the explosion of a massive star after it burns through its fuel — would have to take place within 0.13 light-year of Earth. Yet the closest star big enough to go supernova is nearly 147 light-years away.
Then there are gamma-ray bursts. These explosions are thought to come from especially powerful supernovas or colliding stars. They’re also extremely rare. Over a billion years, there’s only about 1 chance in 3 billion of a gamma-ray burst killing off tardigrades, the researchers calculated.
Loeb and his colleagues published their results July 14 in Scientific Reports.
“Makes me wish I were an extremophile like a tardigrade,” says Edward Guinan. He’s an astrophysicist at Villanova University in Pennsylvania who was not involved in the work. An extremophile is a life form that can survive in harsh environments.
But even tardigrades can’t cheat death forever. In the next seven billion years, the sun will swell into a red giant star. It might engulf Earth, and it will surely sizzle away Earth’s water.
Until then, tardigrades can probably resist any other potential apocalypse. This is exciting to researchers who hope that if there’s life elsewhere in the universe, it lasts long enough for us to find it. Notes Shostak, “Life is tough, once it gets going.”
(for more about Power Words, click here)
alien A non-native organism. (in astronomy) Life on or from a distant world.
asteroid A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
atmosphere The envelope of gases surrounding Earth or another planet.
colleague Someone who works with another; a co-worker or team member.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
extremophile A microorganism that lives in conditions of extreme temperature, acidity, alkalinity or concentrations of chemicals.
global warming The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.
light-year The distance light travels in one year, about 9.48 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
red giant A star having a large diameter and relatively cool surface. It is a stage in a normal star’s life that occurs after it has stopped burning hydrogen. A red giant has a core in which helium is fusing into carbon.
scenario A possible (or likely) sequence of events and how they might play out.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
SETI An abbreviation for the “search for extraterrestrial intelligence,” meaning life on other worlds.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
supernova (plural: supernovae or supernovas) A massive star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.
tardigrade An eight-legged creature not much larger than the period at the end of a sentence. Tardigrades live in many places, including ponds, the sea floor and parts of Antarctica where rock sticks above the ice.
universe The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
vacuum Space with little or no matter in it. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.